<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <script>
        function Animal() {
            
        }

        function Cat(){

        }
        Cat.prototype.__proto__ = Animal.prototype 
        Animal.a = '呵呵'
        var cat = new Cat()
        console.log(cat.a);
        console.log(cat);
        
        

    </script>
</body>

</html>